Rheem Error Code A099: PCB Failure

Severity: Warning
Type: digital display
Where to look: front panel

Warning: This error requires professional repair but poses no immediate safety risk if you keep the system off until serviced.

How to Fix Rheem Code A099

Step 1: Turn off the system at the thermostat and the breaker or disconnect switch. Wait 5 minutes, then turn it back on. If the code clears, a temporary power glitch may have caused it, but still schedule a check.
Step 2: Check the thermostat wiring at the wall. Ensure no bare wires are touching. If you have a nest or other smart thermostat, try pulling it off for 1 minute to reset communication.
Step 3: If the code returns immediately after power-up, or the system still won't start, call a Rheem HVAC pro. Do not attempt to open the electrical panel or replace the board yourselfu2014it requires proper configuration and safety checks.

How to Reset Rheem Code A099

Turn off the unit using the power button on the front panel.
Turn off the gas supply valve.
Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
Restore power at the breaker, then open the gas valve.
Turn the unit back on. If the error returns, the underlying issue needs repair.

What does A099 mean?

The A099 error on Rheem systems indicates a failure of the main control board (PCB). This board controls all system functions, including ignition, fan speed, temperature sensing, and communication with thermostats. When it fails, the system cannot operate correctly or at all. This is typically a hardware failure—often a relay stuck open or closed, a failed capacitor on the board, or a burned trace from a power surge. It can also be triggered by a low-voltage short from the thermostat or zone panel. The board itself is not user-serviceable; it must be replaced by a qualified technician. On Rheem gas furnaces (like the R801T) and air handlers (like the RH2T), this error usually locks the system out, meaning it won't attempt to start again until power is cycled or the thermostat calls again. On Rheem heat pumps (like the RP16), it may also disable the outdoor unit.

Affected Models

Replacement Parts

Part	OEM Number	Est. Cost
Main Control Board (ECM/PCB)	47-103003-01	—
Thermostat / Zone Panel	—	—
Transformer (40VA or higher)	51-117464-01	—

Related Codes on Same Models

Code	Description	Severity
A001	Ignition Failure	Warning
A003	Abnormal Ignition	Warning
A004	False Flame Detection	Warning
A008	Exhaust Temperature High	Warning
A011	No Flame Detected	Warning
A021	Over-Temperature	Warning
A031	Inlet Thermistor Open/Short	Warning
A041	Outlet Thermistor Open/Short	Warning
A043	Water Level Error	Warning
A051	Fan Motor Abnormality	Warning